1. Field of the Invention
This invention relates to bonded fluff structures suitable for use as an absorbent material in personal care absorbent articles including diapers, feminine pads, incontinence garments, and training pants which is required to handle relatively large amounts of discharged body fluids, especially repeated discharges of relatively large amounts of fluid in relatively short periods of time, and a method for producing the same. More particularly, this invention relates to a fiberization process for producing such bonded fluff structures. In addition, this invention relates to a method for producing three-dimensional and density gradient bonded fluff structures for use in personal care absorbent articles.
2. Description of Prior Art
Personal care absorbent products such as diapers, feminine pads, adult incontinence products, and training pants often include a layer of absorbent material and a backing layer or moisture barrier which is impervious to fluid. The absorbent material includes a surface for contacting the body of the user so that body fluids are absorbed into the product and are contained by a moisture barrier.
Such absorbent materials are frequently formed as nonwoven fibrous webs, for example, fluff/binder/superabsorbent composite matrix structures. In order to maintain proper integrity when adhered to distribution materials to allow undisrupted capillarity across the boundary between such absorbent material structures and the distribution materials, and through the absorbent structure, it is necessary to bond the absorbent structure.
Conventionally, the body contacting surface of the absorbent materials in personal care absorbent articles is substantially flat and uniform. There are, however, several advantages to using a textured body contacting surface, such as a greater absorbent surface area and improved anatomical fit. The method of this invention is suitable for forming contoured fibrous webs or pads which have an increased weight of material in selected regions. When forming pads of absorbent material, the regions having the greater weight of material generally have a corresponding greater degree of absorbency. Such contoured absorbent pads are particularly useful in articles that are subjected to a greater fluid loading in certain xe2x80x9ctargetxe2x80x9d areas than in other areas. For example, in a baby diaper comprised of an absorbent bat or pad located between a liquid pervious inner layer and a liquid impervious outer layer, the crotch and front areas of the diaper are more heavily wetted by the infant than the areas closer to the infant""s waist or back. A similar situation may also arise in the case of wound dressings, incontinence garments, and feminine sanitary napkins.
Developments in nonwoven technology have made tremendous strides over the past several years. Today, there exists a wide variety of technologies for forming nonwoven materials including meltblowing, spunbonding, melt spinning, solution spinning, carding, melt spraying, and wet/dry air laying. Many of these technologies are used individually to form single component materials. As an example, spunbonding is used to form nonwoven materials which can be used in such articles as workwear and personal care products including diapers. Meltblowing can be used to generate fine pore structures adaptable for use as filter media or absorbents for oil and other liquids. Air laying can be used to form such products as fibrous wood pulp bats for use as absorbents in diapers and sanitary napkins. In contrast to such processes which produce single component materials, the method of this invention is suitable for producing multicomponent materials.
Diaper dermatitis is a skin condition resulting from the prolonged contact of wet occlusive diapers with the skin of the wearer. This prolonged contact can lead to excessive hydration of the outermost skin layer, thereby reducing the skin""s ability to function as a barrier. As a result, there is an increase in the permeation of irritants, susceptibility of the skin to physical damage, and invasion of the skin by microorganisms. Maintaining a normal skin hydration level helps the skin maintain its optimum barrier properties. Thus, it is important that personal care absorbent articles, to the extent possible, prevent excessive skin hydration while containing body exudates and providing a soft, dry and comfortable feel to the wearer.
Current occlusive absorbent garments with flap liners hold body exudates against the skin of the wearer. Heat and moisture are prevented from escaping from the product due to the close fitting nature of the product designed to prevent leakage. This problem is most severe in the insult region of personal care absorbent products. The flat liner provides a high contact area with the skin which can act as a pathway to conduct back to the skin free liquid that is not locked up by the absorbent core, especially when the product is under pressure at the insult point, because the flat liner cannot provide a sufficient degree of separation of the wearer from the free liquid. In addition, flat liners do not allow the insult region of the personal care absorbent product to communicate with the ambient air to allow humidity to be reduced in the insult region as well as away from the insult region.
There are a number of methods known to those skilled in the art for addressing these problems including the use of breathable back sheets, waist vents, and leg vents. However, these methods suffer from a variety of deficiencies which render them less effective than desired. For example, waist and leg vents through the back sheet tend to either be occluded against the skin or provide leakage pathways. Other known methods include the use of folded absorbent cores or layers under the liner to dry the liner. However, these methods require undesirable process options and economics. Three-dimensional absorbent fabrics, such as those produced in accordance with the method of this invention, can be used to address these issues.
Accordingly, it is one object of this invention to provide a method for bonding of fiber structures which maintain proper integrity when adhered to distribution materials so as to allow undisrupted capillarity across the distribution/fibrous structure boundary.
It is another object of this invention to provide a method of in-situ matrix bonding of fibrous structures using conventional product conversion machines without the addition of lengthy through air bonding ovens.
It is another object of this invention to provide an absorbent material for use in personal care absorbent articles, such as diapers and sanitary pads, having a density gradient.
It is yet another object of this invention to provide a bonded three-dimensional fluff structure for use in personal care absorbent articles.
These and other objects of this invention are achieved by a method for producing bonded fluff structures by which a pulp sheet comprising a material suitable for producing fluff and a heat activatable fiber material is fiberized, producing a mixture of fluff and heat activatable fibers. The mixture of fluff and heat activatable fibers is then contacted with a hot air stream at a flow rate and temperature sufficient to activate the heat activatable fibers without agglomeration of the mixture. The heated mixture is then deposited onto a forming structure, such as a forming wire, resulting in formation of a bonded fluff/fiber composite matrix structure.
In accordance with one embodiment of the method of this invention, the bonded fluff/fiber composite matrix structure is further processed in a manner which imparts a density gradient into the structure, for example, by passing the bonded fluff/fiber composite matrix structure through an embosser.
In accordance with another embodiment of the method of this invention, the bonded fluff/fiber composite matrix structure is shaped to form a bonded three-dimensional fluff structure.